These are a bit arbitrary, and you'll get a different answer depending on whom you ask, but my benchmarks are:
A solid SP ideally has control of 80+, vLh of 60+, vRh of 65+, at least 4 pitches, one of which is in the 80s and the average of which is 50+. Stam is ideally 24+ and Dur is best at 70+, though I've had plenty of luck at 60+. None of these numbers (except for the pitch average) is absolute. Instead, weakness in one area can be remedied by strength in another. Come to think of it, the vRh is relatively inelastic, too. There are just too many Rh batters to skimp on that attribute.
For a solid RP, I would look for control of 80+, vLh and vRh of 70+, and two pitches that average 80+, or three pitches that average 70+. The prototypical solid RP would have a DUR of 70 and a Stam of 30.
For both, velocity and gb/fb are important. A high velocity leads to strike outs, and a high gb/fb leads to more..ahem...groundballs...and fewer homeruns. I tend to value gb/fb a lot, but I know others who skip over it looking for velocity. My tendency may be explained by the fact that I usually field a pretty solid infield defense. If you found a guy who was 70+ in both of those ratings, you could consider yourself lucky. To my eye, however, if you must sacrifice one, sacrifice velocity.
Despite knowing what's most desirable, it's often hard to get a whole staff of solid pitchers at an affordable price. If you'd like an example of what you can make work, take a look at my Pheremoniacs' roster right now. I've made some compromises, but I've been getting pretty solid results (in a division that puts out an MVP on an opponent's team about every other year) for a few seasons now.